The present invention relates to heat exchangers and, in particular, to systems and techniques for determining the location of a leak among a plurality of heat exchange tubes.
There are many applications where leakage into or through tubes must be avoided or detected immediately. One example is the heat exchanger in a nuclear power plant where water within the tubes is heated by liquid sodium. Another example is where sodium heated in a nuclear reactor is used to heat sodium within the tubes which in turn is used to heat water in another heat exchanger. Such a double sodium loop makes leakage of radioactive sodium into the water unlikely. Such leakage must be avoided since the mixing of water and sodium could result in a sodium-water explosion that could scatter radioactive materials under high heat and pressure. Thus, the early detection of leakage is very important for these and other applications.
In a known heat exchanger, (U.S. Pat. No. 4,192,373) a tube sheet employs many rows of tube holes. This known heat exchanger has duplex heat exchange tubes sealed to its tube holes so that leaks in the tubes migrate through the space between the inner and outer wall of the duplex tube to tube holes. A lateral bore extending between rows of these tube holes has a branch channel communicating with the tube holes on either side of the lateral bore. In this way a leak could be isolated to a group of tubes. Moreover, because the junctures between the lateral bore and tube holes are evenly spaced along the lateral bore, a leak detector inserted through the bore can isolate a leak to one particular tube hole.
It is also known to employ a grid of leak detecting pipes in a pile of moderating material in an atomic reactor. The pipes are arranged in a rectangular grid at the face of the material with its intersections near the drainage ducts of the pile. The leak detecting pipes are arranged one for each horizontal row and for each vertical column of drainage ducts. Each leak detecting pipe samples the combined leakage from its associated row or column of drainage ducts. Accordingly, the leak detecting pipes can determine the coordinates of a leak by determining its row and column. However, this type of leak detecting system does not consider how leaks can be detected in a heat exchanger employing heat exchange tubes and tube sheets.
Accordingly, there is a need for a leak detection system which can quickly and simply identify which one of a plurality of heat exchange tubes in a heat exchanger is leaking.